Ice making drum for drum type ice making machine

ABSTRACT

An ice making drum with an improved ice making performance includes a cylindrical drum body, rotational shafts, and shaft members respectively provided at the end faces of the drum body. The drum body has refrigerant flow passages which are each defined by an outer wall portion forming an outer surface, an internal wall portion set apart from the outer wall portion inwardly in a radial direction, and adjoining partition portions extending between the outer wall portion and the internal wall portion. The whole drum body is integrally formed of the same metallic material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ice making drum for a drum type ice making machine, which is configured to be rotatably disposed around a horizontal axis with a part of the ice making drum soaked in ice making water retained in an ice making tank, and produce ice on the outer surface of the ice making drum as a refrigerant is supplied thereto from a freezer and cooled.

2. Description of the Related Art

As means for producing a lot of ice pieces, there is a drum type ice making machine as disclosed in Japanese Patent Publication No. Sho 56-18865. As shown in FIG. 8, a cylindrical ice making drum 14 is rotatably disposed inside an ice making tank 12 retaining ice making water in a drum type ice making machine 11. In the drum type ice making machine 11, a layer of ice is grown on the outer surface (ice making surface) as the ice making drum 14 is rotated while supplying a refrigerant into the ice making drum 14 from a freezer 20, connected with a compressor CM, a condenser CD, an expansion valve EV, etc., and cooling the refrigerant. A cutter 29 is disposed with its blade tip set close to the outer surface of the ice making drum 14. Ice produced on the outer surface of the ice making drum 14 is removed with the cutter 29, and the produced ice pieces are discharged into an ice storage room (not shown). That is, the ice making drum 14 has the functions of both an evaporator which carries out heat exchange between the refrigerant flowing therein and the outer surface thereof to cool the outer surface, and an ice making part which produces ice blocks.

As shown in FIG. 9, the ice making drum 14 is configured by coaxially fitting a columnar core member 16 into a cylindrical jacket 15. A plastic material which has a heat insulating property is used for the core member 16, whereas a metallic material excellent in thermal conductivity is used for the jacket 15 to be an ice making surface. A groove 16 a is spirally formed in the circumferential surface of the core member 16. A refrigerant flow passage 18 is spirally defined in the ice making drum 14 by the inner surface of the jacket 15, and the wall portion of the core member 16 which defines the groove 16 a as the circumferential surface of the core member 16 abuts on the inner surface of the jacket 15. In this manner, the ice making drum 14 is made by combining two members with different thermal conductivities, thereby forming the refrigerant flow passage 18.

As shown in FIG. 8, rotational shafts 14 a and 14 b which protrude from the respective end faces of the ice making drum 14 are rotatably supported at the ice making tank 12, and the ice making drum 14 is rotated in a predetermined direction as one of the rotational shafts 14 a and 14 b is rotated by a drive mechanism (not shown). A supply passage 22 to be connected to the downstream of the expansion valve EV in the freezer 20 is provided at one rotational shaft 14 a, and the supply passage 22 is communicated with the upstream of the refrigerant flow passage 18 via a first bore hole 16 b that penetrates the core member 16 radially. On the other hand, a return passage 24 to be connected to the upstream of the compressor CM in the freezer 20 is provided at the other rotational shaft 14 b, and the return passage 24 is communicated with the downstream of the refrigerant flow passage 18 via a second bore hole 16 c that penetrates the core member 16 radially. At the time of the ice making operation, a circulation cycle is formed in which the refrigerant supplied to the supply passage 22 from the freezer 20 is led to the refrigerant flow passage 18 to cool the circumferential surface of the ice making drum 14 in the process in which the refrigerant spirally flows in the refrigerant flow passage 18, and is returned to the freezer 20 via the return passage 24 of the other rotational shaft 14 b.

In order to produce ice blocks efficiently on the outer surface of the ice making drum 14, it is necessary to cool the whole ice making drum 14 uniformly. In this respect, the ice making drum 14 is configured in such a way that providing the spiral refrigerant flow passage 18 causes the refrigerant to generally circulate. This requires that the groove 16 a formed in the circumferential surface of the core member 16 should be made into a complicated shape like a spiral shape. In addition, the bore holes 16 b and 16 c which communicate with the supply passage 22 and the return passage 24 of the rotational shafts 14 a and 14 b should be formed at the upstream and downstream ends of the groove 16 a. It is pointed out that although the plastic material for the core member 16 is itself easy to process, it takes time to process the groove 16 a and the bore holes 16 b and 16 c for the shapes and directions of the groove 16 a and the bore holes 16 b and 16 c are complicated, thus making the ice making drum 14 expensive.

As mentioned above, the ice making drum 14 has the refrigerant flow passage 18 defined by fitting the core member 16 inside the jacket 15, so that if a clearance is made between the inner surface of the jacket 15 and the circumferential surface of the core member 16, the refrigerant flow passage 18 is short-circuited, disabling acquisition of the desired cooling performance as a whole. This demands high accuracy on the inner circumferential dimension of the jacket 15 and the size of the outer circumferential dimension of the core member 16, which leads to an increase in cost. The work of assembling the jacket 15 and the core member 16 is carried out by the so-called cold fitting which uses the difference in linear expansion coefficient between the jacket 15 and the core member 16. That is, while the jacket 15 made of a metallic material with a high linear expansion coefficient is heated to expand, the core member 16 made of a plastic material with a low linear expansion coefficient is cooled for contraction, and was shrunk, and they are fitted to each other in that state. The contracted jacket 15 makes the connection of the core member 16 firm in the thus formed ice making drum 14 in a use state (ordinary temperature), raising the problem that while the short-circuiting of the refrigerant flow passage 18 can be prevented, the number of assembly steps increases, so that it takes time in controlling the temperatures of the individual members 15, 16 at the time of the assembling work. There also is a need for equipment for heating or cooling these members 15, 16, which also increases the manufacturing cost.

Since the core member 16 is made of a plastic material with a low thermal conductivity, heat conduction is difficult to occur between itself and the jackets 15. What is more, the efficiency of heat exchange between the side wall portion of the refrigerant flow passage 18 which is formed by the core member 16, and the refrigerant which circulates in the refrigerant flow passage 18 is poor, so that heat exchange with the jacket 15 through the side wall portion cannot be expected. That is, since the refrigerant circulating in the refrigerant flow passage 18 just substantially exchanges heat with the jackets 15 which faces the refrigerant flow passage 18, the ice making drum 14 cannot fully demonstrate the refrigeration performance as an evaporator.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide an ice making drum for a drum type ice making machine which is proposed to favorably overcome the inherent problems of the ice making drum for the drum type ice making machine according to the prior art, is easy to manufacture and is excellent in ice-making efficiency.

To overcome the problems and achieve the intended object, according to the invention, there is provided an ice making drum for a drum type ice making machine, which is configured to be rotatably disposed around a horizontal axis with a part of the ice making drum soaked in ice making water retained in an ice making tank, and produce ice on an outer surface of the ice making drum as a refrigerant is supplied thereto from a freezer and cooled, the ice making drum comprising:

-   a drum body having refrigerant flow passages which are each defined     by an outer wall portion forming an outer surface, an internal wall     portion set apart by a predetermined distance from the outer wall     portion inwardly in a radial direction, and partition portions     extending between the outer wall portion and the internal wall     portion and adjoining in a circumferential direction, and are     arranged along a circumferential surface of the drum body and     penetrating the circumferential surface in an axial direction, the     drum body being integrally formed of a same metallic material; and -   a pair of shaft members which are respectively attached to both end     faces of the drum body and at least one of which is provided with a     refrigerant circulation passage to the refrigerant flow passages.

According to the ice making drum for the drum type ice making machine according to the invention, the refrigerant circulating in the refrigerant flow passage favorably exchanges heat with the four side wall portions, so that the performance as an evaporator becomes higher, making it possible to improve the ice-making efficiency. Further, since the refrigerant flow passage formed in the drum body is a simple through hole which extends in the axial direction, it can be formed easily, making it possible to reduce the manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an ice making drum for a drum type ice making machine according to a preferable embodiment of the invention;

FIG. 2 is an exploded perspective view showing the ice making drum according to the embodiment with its part cut away;

FIG. 3 is a diagram as seen from an arrow A in FIG. 2;

FIG. 4 is a cross-sectional view of FIG. 2 along a line B-B;

FIG. 5 is a cross-sectional view of FIG. 2 along a line C-C;

FIG. 6 is an enlarged view of a portion D in FIG. 4;

FIG. 7 is a cross-sectional view showing one example of an ice making mechanism in the drum type ice making machine;

FIG. 8 is a schematic cross-sectional view showing the conventional ice making drum for a drum type ice making machine; and

FIG. 9 is an exploded perspective view showing the conventional ice making drum with its part cut away.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An ice making drum for a drum type ice making machine according to the invention is described below by way of a preferred embodiment with reference to the accompanying drawings. For the sake of descriptive convenience, same or like reference numerals are used for those components which are identical to those of the drum type ice making machine as shown in FIGS. 8 and 9 to avoid their redundant descriptions.

Embodiment

As shown in FIG. 1, a drum type ice making machine 10 according to the embodiment has an ice making mechanism which comprises an ice making tank 12 retaining a predetermined amount of ice making water, and a cylindrical ice making drum 30 disposed in the ice making tank 12 in such a way as to be rotatable about the horizontal axis with its part soaked in the ice making water. The ice making drum 30 is connected to a freezer 20 connected with a compressor CM, a condenser CD, an expansion valve EV, etc. by a refrigerant piping 20 a; and functions as an evaporator in a refrigerant circulation cycle as a part of the freezer 20. Specifically, in the freezer 20, the ice making drum 30 is positioned downstream of the expansion valve EV, and upstream of the compressor CM, and is connected to the expansion valve EV and the compressor CM via the refrigerant piping 20 a.

As shown in FIG. 2, the ice making drum 30 basically comprises a cylindrical drum body 32 formed of a metallic material excellent in thermal conductivity, such as an aluminum alloy, and shaft members 40 and 50 respectively disposed at the both axial ends of the drum body 32. A rotational shaft 42, 52 is protrusively provided at the axial center of one end face of each shaft member 40, 50 respectively so as to extend in the axial direction of the ice making drum 30. The ice making drum 30 is horizontally disposed with the rotational shafts 42 and 52 rotatably supported at bearings (not shown) provided at the opposing wall surfaces of the ice making tank 12 (see FIG. 1).

The drum body 32 has a plurality of refrigerant flow passages 34 extending along the circumferential surface arranged in the circumferential direction at predetermined intervals and in a circle about the axis of the drum body 32, and a hollow part 36 penetrating in the axial direction at the center section (see FIG. 3 or FIG. 4). Each refrigerant flow passage 34 is defiried by an outer wall portion 32 a which forms the outer surface of the drum body 32 (ice making drum 30), an inner wall portion 32 b set apart by a predetermined distance from the outer wall portion 32 a inwardly in the radial direction, and a pair of partition portions 32 c, 32 c axially extending, apart from each other in the circumferential direction, between the outer wall portion 32 a and the internal wall portion 32 b. Each refrigerant flow passage 34 is formed so as to linearly penetrate the drum body 32 in the axial direction thereof, and to be open at both ends (see FIG. 2). The hollow part 36 is formed inside the inner wall portion 32 b in the drum body 32, and the drum body 32 has a double cylindrical tube structure which has the outer wall portion 32 a and the inner wall portion 32 b tube walls. The refrigerant flow passages 34 and the hollow part 36 are provided open at the same time as the outer shape of the drum body 32 by extrusion molding, and the whole drum body 32 having the outer wall portion 32 a to be the ice making surface, the inner wall portion 32 b, and the partition portions 32 c is integrally and seamlessly formed of a single metallic material.

Each of the partition portions 32 c is configured so as to extend in the radial direction of the drum body 32 and be connected to the outer wall portion 32 a and the inner wall portion 32 b. Each partition portion 32 c has its width so set as to be approximately constant from the outer wall portion 32 a side from the inner wall portion 32 b side, so that both wall surfaces of each partition portion 32 c are in parallel to each other. The cross section of the drum body 32 which is cut off in the radial direction thereof is formed in an approximately quadrangular shape (see FIG. 4). More particularly, a plurality of partition portions 32 c are formed radially around the axial line of the drum body 32, so that the space between the adjoining partition portions 32 c, 32 c becomes wider in the direction from the inner wall portion 32 b toward the outer wall portion 32 a. As shown in FIG. 6, therefore, each refrigerant flow passage 34 has a fan-shaped quadrangle shape such that an arc size L1 of the outer wall portion 32 a which faces each refrigerant flow passage 34 is larger than an arc size L2 of the inner wall portion 32 b which faces the refrigerant flow passage 34, so that each refrigerant flow passage 34 expands outward in the radial direction. Further, the internal wall portion 32 b has a thickness T2 set thicker than a thickness T1 of the outer wall portion 32 a.

Every other partition portions 32 c in the circumferential direction which face each end face of the drum body 32 are recessed inwardly in the axial direction, providing, at each end face of the drum body 32, communication passages 38 each pair of which connect adjoining refrigerant flow passages 34, 34 (see FIG. 2 or FIG. 3). The partition portions 32 c recessed at one end face of the drum body 32 is shifted by one in the circumferential direction with respect to the partition portion 32 c which is recessed at the other end face of the drum body 32. That is, the drum body 32 is configured in such a way that the communication passages 38 are provided at both end faces of the drum body 32 alternately, shifted from one another by one refrigerant flow passage 34, so that the refrigerant circulates through the refrigerant flow passages 34 connected by the communicating passages 38 to meandering state (see FIG. 2). In the drum body 32 according to the embodiment, the refrigerant flow passage 34 which serves as an inlet end for the refrigerant and the refrigerant flow passage 34 which serves as an outlet end for the refrigerant adjoin each other, and both end faces of the partition portion 32 c located therebetween is not recessed.

The hollow part 36 is filled up with a functional material for preventing occurrence of dew condensation and rusting, thus inhibiting degradation of the ice making drum 30. A heat insulating material which is formed by filling a foaming agent having a heat insulating property, such as urethane, a drying agent, such as silica gel, or an inactive gas, such as nitrogen, is adopted as the functional material; a mode in which a heat insulator 37 is filled into the hollow part 36 is employed in the embodiment by way of example.

Each of the shaft members 40 and 50 basically comprises a disc-shaped cover part 43, 53 which is coaxially aligned with the end face of the drum body 32, and the rotational shaft 42, 52 which protrudes outward in the axial direction of the cover part 43, 53 from the axial center thereof. In the embodiment, “first” is affixed to one shaft member 40 connected to the freezer 20 and the components of this shaft member 40, and “second” is affixed to the other shaft member 50 and the components of this shaft member 50 to distinguish the former from the latter. The shaft member 40, 50 may be constructed by integrally forming the cover part 43, 53 and the rotational shaft 42, 52, or by combining separate members.

The first shaft member 40 is provided with a supply passage (circuit) 46 which guides the refrigerant from the freezer 20 to the refrigerant flow passage 34, and the return passage (circuit) 47 which returns the refrigerant, circulated through the refrigerant flow passage 34, to the freezer 20, and serves as an inlet part and an outlet part for the refrigerant in the ice making drum 30 (see FIG. 1). The first shaft member 40 has a supply opening 44 and a return opening 45 provided at that inner surface of the first cover part 43 which is connected to the end face of the drum body 32 respectively according to the refrigerant flow passage 34 serving as the refrigerant inlet end and according to the refrigerant flow passage 34 serving as the refrigerant outlet end (see FIG. 2 or FIG. 5). The first rotational shaft 42 has a double tube structure where a return line 47 a, which returns the refrigerant circulated through the refrigerant flow passage 34 to the freezer 20, is defined in the center thereof in the axial direction, and a supply line 46 a, which supplies the refrigerant to the outside of the return line 47 a from the freezer 20, is provided coaxial with the return line 47 a. At that portion of the first rotational shaft 42 which protrudes from the ice making tank 12, the refrigerant piping 20 a connected to the expansion valve EV in the freezer 20 is communicated with the supply line 46 a, and the refrigerant piping 20 a connected to the compressor CM is communicated with the return line 47 a. The first cover part 43 has a supply passage 46 b defined therein which connects the supply opening 44 to the end of the supply line 46 a facing the interior of the cover part 43, and extends radially (see FIG. 5). Further, the first cover part 43 has a return passage 47 b defined therein which connects the return opening 45 to the end of the return line 47 a facing the interior of the cover part 43, and extends radially. In the first shaft member 40, therefore, the supply passage 46 is formed by the supply line 46 a and the supply passage 46 b, and the return passage 47 is formed by the return line 47 a and the return passage 47 b.

That portion of the second rotational shaft 52 of the second shaft member 50 which protrudes outward from the ice making tank 12 is connected a drive mechanism M, and is configured to transmit the rotation of the drive mechanism M to rotate the ice making drum 30 (see FIG. 1). A gear motor or the like is adopted as the drive mechanism M.

The first shaft member 40 and the second shaft member 50 are attached to the corresponding end faces by fastening screws, inserted in through holes formed in the cover parts 43 and 53, into screw holes formed in the inner wall portion 32 b of the drum body 32. At this time, in the ice making drum 30, the openings open to the end faces of the drum body 32 in the hollow part 36 are respectively closed by the cover parts 43 and 53 of both shaft members 40 and 50, making the sealed space in the hollow part 36. In the ice making drum 30, the portions which are recessed in the end faces of the partition portions 32 c in the drum body 32 are closed by the individual cover parts 43 and 53, and the communicating passage 38 is formed in airtight between the end face of the drum body 32, and the cover parts 43 and 53. In the ice making drum 30, the adjoining set of refrigerant flow passages 34 is communicated with each other by the communicating passage 38. Further, in the ice making drum 30, the supply opening 44 of the first cover part 43 in the first shaft member 40 is aligned with the opening of the refrigerant flow passage 34 serving as the refrigerant inlet end, and the return opening 45 is aligned with the opening of the refrigerant flow passage 34 serving as the refrigerant outlet end. Accordingly, the ice making drum 30 is configured in such a way that the refrigerant circulating passage is formed in a sequential manner in a meandering form in which the refrigerant flow passage 34 is used as a straight-line portion, and the communicating passage 38 is used as a returning portion, so that the refrigerant from the supply passage 46 circulates in one of the circumferential direction while alternately flowing in the axial direction to one side of a circumferential direction, and reaches the return passage 47.

As shown in FIG. 7, a water supply opening 26 which is connected in communication to a water supply piping (not shown) derived from an external water system on a wall surface is provided in the ice making tank 12, so that releasing a water supply valve (not shown) intervened in the water supply piping causes the ice making water (tap water) to be supplied into the ice making tank 12 from the water supply opening 26. A water level sensor 27, such as a float switch, for detecting the amount of ice making water (water level), is disposed inside the ice making tank 12, and the water level in the ice making tank 12 is kept constant by controlling the opening and closing of the water supply valve according to the detected state of the water level by the sensor 27.

A chute 28 which communicates with the ice storage room (not shown) provided under is disposed at one side (right-hand side in FIG. 7) of the ice making tank 12, and the chute 28 and the ice making tank 12 are configured so as to communicate with each other at the upper portion of the right-hand side of the tank 12. The cutter 29 is disposed between the opposite wall surfaces of the ice making tank 12 at portions with which the chute 28 communicates in such a way that the cutter 29 extends in the axial direction of the ice making drum 30 with its blade tip facing toward the outer surface of the ice making drum 30 which sticks out of the ice making water. When the ice making drum 30 rotates in the ice making operation, the cutter 29 hits against the ice produced on the circumferential surface of the ice making drum 30, separating the ice thinly. The top surface of the cutter 29 has a slope 29 a which is inclined downward as it comes away from the ice making drum 30, so that the ice pieces separated with the cutter 29 slide on the cutter's upper surface and the slope 29 a to be guided to the chute 28.

Operation of Embodiment

Next, the operation of the ice making drum for the drum type ice making machine according to the embodiment is explained. When the ice making operation of the drum type ice making machine 10 is started, the drive mechanism M is driven to continuously rotate the ice making drum 30 via the second rotational shaft 52. The freezer 20 is driven simultaneously, and the evaporated refrigerant compressed from the compressor CM is liquefied by the condenser CD. The liquefied refrigerant is further decompressed by the expansion valve EV, and is led into the supply passage 46 of the first rotational shaft 42. The refrigerant is supplied to the refrigerant inlet end of the refrigerant flow passage 34 connected to the supply opening 44 from the supply passage 46, and is subjected to heat exchange with the drum body 32 to be sequentially evaporated in the process in which the refrigerant circulates in a meandering form in the circulation passage which consists of the refrigerant flow passage 34 and the communicating passage 38. Accordingly, the refrigerant takes heat from the drum body 32, cooling the outer surface of the ice making drum 30 (drum body 32). As the ice making drum 30 is cooled, a layer of ice is grown on that portion of the ice making drum 30 which is soaked in the ice making water. As the ice comes out of the ice making water according to the rotation of the drum 30, the ice becomes super-cooled dry ice which does not contain moisture. The ice is exfoliated with the cutter 29 to become thin lepidic ice pieces, which slide on the slope 29 a to be guided to the chute 28, and fall through the chute 28 to be discharged into the ice storage room. The refrigerant in the refrigerant flow passage 34, which has exchanged heat with the drum body 32 to be vaporized, arrives at the return passage 47 via the return opening 45 of the first cover part 43 in the first shaft member 40, and is returned to the freezer 20 from the return passage 47.

Since the refrigerant flow passage 34 is formed in such a way that the refrigerant circulates in the axial direction, the refrigerant can uniformly cool the outer surface of the ice making drum 30 in the axial direction. That is, ice can be produced uniformly on the outer surface of the ice making drum 30 in the axial direction, making it possible to eliminate local concentration of the load acting on the cutter 29 at the time of exfoliating ice with the cutter 29. It is therefore possible to avoid deformation, partial wearing or the like of the cutter 29 and the bearings.

In the ice making drum 30, the outer wall portion 32 a, the inner wall portion 32 b, and the partition portions 32 c and 32 c which define the refrigerant flow passages 34 provided in the drum body 32 are integrally formed of a metallic material with good thermal conductivity. This allows the refrigerant circulating in the refrigerant flow passage 34 to favorably exchange heat with the four side walls 32 a, 32 b, 32 c, and 32 c, so that evaporation of a liquefied refrigerant is carried out smoothly. This can improve the performance as the evaporator in the ice making drum 30, thus improving the ice-making efficiency. In addition, since the outer wall portion 32 a, the inner wall portion 32 b, and the partition portions 32 c and 32 c are not connected by separate members, heat conduction is not interfered at the connecting faces, and is carried out well among the wall portions 32 a, 32 b, 32 c, and 32 c. That is, the outer wall portion 32 a which serves as the ice making surface of the ice making drum 30 is cooled not only by direct heat exchange with the refrigerant in the refrigerant flow passage 34 but also by heat exchange with the partition portions 32 c and 32 c, and the inner wall portion 32 b via the partition portions 32 c and 32 c, making it possible to improve the ice-making efficiency.

As the performance of the ice making drum 30 as the evaporator is improved, the overall ice making performance required can be maintained even if the performance of the compressor CM is lowered. This makes it possible to reduce the cost for the machine and achieve power saving. Even for the ice making drum 30 with the conventional configuration of the same performance of structure, the embodiment can down-size the compressor CM or the ice making drum 30, also making the machine room or the ice making tank 12 more compact. This makes it possible to reduce the strengths required of accessory members, such as the stand of the compressor CM and the bearings of the ice making drum 30. Further, the weight of the drum type ice making machine 10 can also be reduced.

Because the refrigerant circulation passage formed in the ice making drum 30 is structured so that the refrigerant flow passages 34 linearly penetrating in the axial direction of the drum body 32 are connected by the communicating passages 38, and the refrigerant flow passages 34 are merely through holes, they can be formed easily, making it possible to reduce the manufacturing cost. Further, the refrigerant flow passage 34 is defined by the integrally formed wall portions 32 a, 32 b, 32 c, and 32 c, short-circuiting does not occur between the adjacent refrigerant flow passages 34, 34. Furthermore, since the drum body 32 is a single member, not formed by a combination of members as explained in the Description of the Related Art, the drum body 32 does not demand high dimensional accuracy, which also leads to cost reduction.

The use of extrusion molding as a method of manufacturing the drum body 32 can allow the refrigerant flow passage 34 and the hollow part 36 to be formed together with the formation of the outer shape, so that the post processing of forming the refrigerant flow passage 34 and the step of assembling the jacket and the core member as explained in the Description of the Related Art can be skipped.

The refrigerant flow passage 34 is formed to have an approximately quadrangle cross section which expands outward in the radial direction of the drum body 32, making it possible to secure a wide contact area between the outer wall portion 32 a to be the ice making surface, and the refrigerant. That is, since heat exchange with the refrigerant is preferentially carried out at the outer wall portion 32 a, the ice making performance of the ice making drum 30 can be improved. What is more, the widened cross-sectional area of the refrigerant flow passage 34 brings about a merit of a lower extruding resistance at the time of carrying out extrusion molding, thus ensuring easier molding. In addition, non-uniform cooling can be eliminated by setting the width of the partition portion 32 c constant to make the interval between the adjacent refrigerant flow passages 34 constant, thus making it possible to avoid local concentration of the external force applied to the drum body 32. The formation of the refrigerant flow passage 34 to have an approximately quadrangle cross-sectional shape causes the line connecting the adjacent refrigerant flow passages 34, 34 to be a straight line or an approximate straight line, making machining easier.

As the thickness T2 of the inner wall portion 32 b is set thicker than the thickness T1 of the outer wall portion 32 a, a possible reduction in the strength of the drum body 32 originating from by the formation of a plurality of refrigerant flow passages 34 and the hollow portion 36 can be compensated for by the thick inner wall portion 32 b, making it possible to secure the required overall strength of the drum body 32. Since the strength of the drum body 32 can be maintained by the inner wall portion 32 b, the thickness T1 of the outer wall portion 32 a serving as the ice making surface can be set to the dimension suitable for heat exchange with the refrigerant flowing in the refrigerant flow passages 34. This allows heat exchange with the refrigerant to be preferentially carried out at the outer wall portion 32 a, so that the ice making performance of the ice making drum 30 can be improved. Further, the thermal conductivity of the inner wall portion 32 b becomes lower as compared with that of the outer wall portion 32 a, thus making it possible to prevent dew condensation at the hollow part 36.

The provision of the hollow part 36 reduces the weight of the drum body 32. This can facilitate the handling of the ice making drum 30 at the time of manufacturing the ice making drum 30, and reduce the weight of the ice making machine itself. Further, the power and the drive source which are required to drive the ice making drum 30 can be made smaller, which can lead to reduction in power consumption. Since the heat insulator 37 is enclosed in the hollow part 36, its heat insulation can suppress heat exchange of the hollow part 36 with the refrigerant through the hollow part 36, thereby suppressing cooling of the hollow part 36. This can prevent dew condensation from occurring. As the expansion of the foaming agent pushes the air in the hollow part 36 outside, there is not much oxygen present in the hollow part 36, thus making it possible to prevent the interior of the inner wall portion 32 b from being rusted. The suppression of occurrence of dew condensation in the hollow part 36 this way can also prevent the ice making drum 30 from being broken due to the freezing of condensed dews.

(Modifications)

The present invention is not limited to the configuration of the embodiment, and may also be modified as follows.

-   (1) Although the supply passage and return passage serving as the     circuits for the refrigerant to the refrigerant flow passage are     provided at the first shaft member according to the embodiment, both     of the supply passage and the return passage may be provided at the     second shaft member, or the supply passage may be provided at one     shaft member while the return passage may be provided at the other     shaft member. -   (2) Although one refrigerant circulation passage meandering     sequentially which is formed by connecting the refrigerant flow     passages extending in the axial direction by the communicating     passages is provided in the ice making drum according to the     embodiment, the ice making drum may take a mode such that the     refrigerant is dispersedly supplied to the individual refrigerant     flow passages from one shaft member, is let to flow through the     individual refrigerant flow passages to the other shaft member, and     is gathered at the other shaft member to be returned to the freezer.     Alternatively, the refrigerant circulation passage may be formed in     such a way that the refrigerant is dispersedly supplied to the     individual refrigerant flow passages from one shaft member, is     reciprocated once or multiple times in the axial direction, and is     then gathered at one shaft member or the other shaft member. -   (3) While the drum body is formed by extrusion molding according to     the embodiment, the drum body may be formed by performing boring or     wire cutting on a solid metal blank formed in a columnar shape. In     this case too, the whole drum body is made of a single metallic     material. Further, casting may be used. -   (4) Although the cross-sectional shape of the refrigerant flow     passage is set to an approximately quadrangular shape according to     the embodiment, it may be a circular shape, an elliptical shape, a     polygonal shape or the like. -   (5) Although the foregoing description of the embodiment has been     given of the configuration in which the shaft members are connected     to the drum body by screws by way of example, other modes can be     taken, such as welding of the shaft members to end faces of the     inner wall portion or the like of the drum body, and connection of     the shaft members to the drum body by fitting engagement means,     provided at the inner surface of the cover portion, into engagement     means provided at the inner wall portion. At this time, if the inner     wall portion of the drum body is formed thick, the inner wall     portion can be effectively used as a welding face or a mount surface     for the engagement means. -   (6) While the communicating passage is provided by recessing the end     face of the partition portion of the drum body according to the     embodiment, the communicating passage may be provided by recessing     the inner surface of the cover part of the shaft member which     corresponds to the opening of the refrigerant flow passage. It is     also possible to take a mode in which the end face of the partition     portion is recessed and the inner surface of the cover part is     recessed. -   (7) A drier if used as the functional material to be filled in the     hollow portion can dry the interior atmosphere of the hollow portion     and prevent occurrence of dew condensation even if the hollow     portion is cooled. In case of using an inactive gas, filling the     inactive gas pushes the air out of the hollow portion, there is not     much oxygen present in the hollow part, thus making it possible to     prevent the interior of the inner wall portion from being rusted. -   (8) While an aluminum alloy is used as the metallic material for the     drum body according to the embodiment, copper or another metal alone     or an alloy thereof can be used. 

1. An ice making drum for a drum type ice making machine, which is configured to be rotatably disposed around a horizontal axis with a part of the ice making drum soaked in ice making water retained in an ice making tank, and produce ice on an outer surface of the ice making drum as a refrigerant is supplied thereto from a freezer and cooled, the ice making drum comprising: a drum body having refrigerant flow passages which are each defined by an outer wall portion forming an outer surface, an internal wall portion set apart by a predetermined distance from the outer wall portion inwardly in a radial direction, and partition portions extending between the outer wall portion and the internal wall portion and adjoining in a circumferential direction, and are arranged along a circumferential surface of the drum body and penetrating the circumferential surface in an axial direction, the drum body being integrally formed of a same metallic material; and a pair of shaft members which are respectively attached to both end faces of the drum body and at least one of which is provided with a refrigerant circulation passage to the refrigerant flow passages.
 2. The ice making drum according to claim 1, wherein a cross section of the drum body in a radial direction thereof is formed in an approximately quadrangular shape which expands outward in the radial direction.
 3. The ice making drum according to claim 1, wherein a thickness of the internal wall portion is set thicker than a thickness of the outer wall portion.
 4. The ice making drum according to claim 2, wherein a thickness of the internal wall portion is set thicker than a thickness of the outer wall portion. 